codex-tools: extract responses API tool models (#16031)

## Why

The previous extraction steps moved shared tool-schema parsing into
`codex-tools`, but `codex-core` still owned the generic Responses API
tool models and the last adapter layer that turned parsed tool
definitions into `ResponsesApiTool` values.

That left `core/src/tools/spec.rs` and `core/src/client_common.rs`
holding a chunk of tool-shaping code that does not need session state,
runtime plumbing, or any other `codex-core`-specific dependency. As a
result, `codex-tools` owned the parsed tool definition, but `codex-core`
still owned the generic wire model that those definitions are converted
into.

This change moves that boundary one step further. `codex-tools` now owns
the reusable Responses/tool wire structs and the shared conversion
helpers for dynamic tools, MCP tools, and deferred MCP aliases.
`codex-core` continues to own `ToolSpec` orchestration and the remaining
web-search-specific request shapes.

## What changed

- added `tools/src/responses_api.rs` to own `ResponsesApiTool`,
`FreeformTool`, `ToolSearchOutputTool`, namespace output types, and the
shared `ToolDefinition -> ResponsesApiTool` adapter helpers
- added `tools/src/responses_api_tests.rs` for deferred-loading
behavior, adapter coverage, and namespace serialization coverage
- rewired `core/src/tools/spec.rs` to use the extracted dynamic/MCP
adapter helpers instead of defining those conversions locally
- rewired `core/src/tools/handlers/tool_search.rs` to use the extracted
deferred MCP adapter and namespace output types directly
- slimmed `core/src/client_common.rs` so it now keeps `ToolSpec` and the
web-search-specific wire types, while reusing the extracted tool models
from `codex-tools`
- moved the extracted seam tests out of `core` and updated
`codex-rs/tools/README.md` plus `tools/src/lib.rs` to reflect the
expanded `codex-tools` boundary

## Test plan

- `cargo test -p codex-tools`
- `cargo test -p codex-core --lib tools::spec::`
- `cargo test -p codex-core --lib tools::handlers::tool_search::`
- `just fix -p codex-tools -p codex-core`
- `just argument-comment-lint`

## References

- [#15923](https://github.com/openai/codex/pull/15923) `codex-tools:
extract shared tool schema parsing`
- [#15928](https://github.com/openai/codex/pull/15928) `codex-tools:
extract MCP schema adapters`
- [#15944](https://github.com/openai/codex/pull/15944) `codex-tools:
extract dynamic tool adapters`
- [#15953](https://github.com/openai/codex/pull/15953) `codex-tools:
introduce named tool definitions`

codex-rs/core/src/client_common.rs

@@ -157,14 +157,16 @@ fn strip_total_output_header(output: &str) -> Option<(&str, u32)> {
 }
 
 pub(crate) mod tools {
-    use crate::tools::spec::JsonSchema;
     use codex_protocol::config_types::WebSearchContextSize;
     use codex_protocol::config_types::WebSearchFilters as ConfigWebSearchFilters;
     use codex_protocol::config_types::WebSearchUserLocation as ConfigWebSearchUserLocation;
     use codex_protocol::config_types::WebSearchUserLocationType;
-    use serde::Deserialize;
+    pub(crate) use codex_tools::FreeformTool;
+    pub(crate) use codex_tools::FreeformToolFormat;
+    use codex_tools::JsonSchema;
+    pub(crate) use codex_tools::ResponsesApiTool;
+    pub(crate) use codex_tools::ToolSearchOutputTool;
     use serde::Serialize;
-    use serde_json::Value;
 
     /// When serialized as JSON, this produces a valid "Tool" in the OpenAI
     /// Responses API.
@@ -256,59 +258,6 @@ pub(crate) mod tools {
             }
         }
     }
-
-    #[derive(Debug, Clone, Serialize, Deserialize, PartialEq)]
-    pub struct FreeformTool {
-        pub(crate) name: String,
-        pub(crate) description: String,
-        pub(crate) format: FreeformToolFormat,
-    }
-
-    #[derive(Debug, Clone, Serialize, Deserialize, PartialEq)]
-    pub struct FreeformToolFormat {
-        pub(crate) r#type: String,
-        pub(crate) syntax: String,
-        pub(crate) definition: String,
-    }
-
-    #[derive(Debug, Clone, Serialize, PartialEq)]
-    pub struct ResponsesApiTool {
-        pub(crate) name: String,
-        pub(crate) description: String,
-        /// TODO: Validation. When strict is set to true, the JSON schema,
-        /// `required` and `additional_properties` must be present. All fields in
-        /// `properties` must be present in `required`.
-        pub(crate) strict: bool,
-        #[serde(skip_serializing_if = "Option::is_none")]
-        pub(crate) defer_loading: Option<bool>,
-        pub(crate) parameters: JsonSchema,
-        #[serde(skip)]
-        pub(crate) output_schema: Option<Value>,
-    }
-
-    #[derive(Debug, Clone, Serialize, PartialEq)]
-    #[serde(tag = "type")]
-    pub(crate) enum ToolSearchOutputTool {
-        #[allow(dead_code)]
-        #[serde(rename = "function")]
-        Function(ResponsesApiTool),
-        #[serde(rename = "namespace")]
-        Namespace(ResponsesApiNamespace),
-    }
-
-    #[derive(Debug, Clone, Serialize, PartialEq)]
-    pub(crate) struct ResponsesApiNamespace {
-        pub(crate) name: String,
-        pub(crate) description: String,
-        pub(crate) tools: Vec<ResponsesApiNamespaceTool>,
-    }
-
-    #[derive(Debug, Clone, Serialize, PartialEq)]
-    #[serde(tag = "type")]
-    pub(crate) enum ResponsesApiNamespaceTool {
-        #[serde(rename = "function")]
-        Function(ResponsesApiTool),
-    }
 }
 
 pub struct ResponseStream {

codex-rs/core/src/client_common_tests.rs

@@ -197,49 +197,3 @@ fn reserializes_shell_outputs_for_function_and_custom_tool_calls() {
         ]
     );
 }
-
-#[test]
-fn tool_search_output_namespace_serializes_with_deferred_child_tools() {
-    let namespace = tools::ToolSearchOutputTool::Namespace(tools::ResponsesApiNamespace {
-        name: "mcp__codex_apps__calendar".to_string(),
-        description: "Plan events".to_string(),
-        tools: vec![tools::ResponsesApiNamespaceTool::Function(
-            tools::ResponsesApiTool {
-                name: "create_event".to_string(),
-                description: "Create a calendar event.".to_string(),
-                strict: false,
-                defer_loading: Some(true),
-                parameters: crate::tools::spec::JsonSchema::Object {
-                    properties: Default::default(),
-                    required: None,
-                    additional_properties: None,
-                },
-                output_schema: None,
-            },
-        )],
-    });
-
-    let value = serde_json::to_value(namespace).expect("serialize namespace");
-
-    assert_eq!(
-        value,
-        serde_json::json!({
-            "type": "namespace",
-            "name": "mcp__codex_apps__calendar",
-            "description": "Plan events",
-            "tools": [
-                {
-                    "type": "function",
-                    "name": "create_event",
-                    "description": "Create a calendar event.",
-                    "strict": false,
-                    "defer_loading": true,
-                    "parameters": {
-                        "type": "object",
-                        "properties": {}
-                    }
-                }
-            ]
-        })
-    );
-}

codex-rs/core/src/tools/handlers/tool_search.rs

@@ -1,6 +1,3 @@
-use crate::client_common::tools::ResponsesApiNamespace;
-use crate::client_common::tools::ResponsesApiNamespaceTool;
-use crate::client_common::tools::ToolSearchOutputTool;
 use crate::function_tool::FunctionCallError;
 use crate::mcp_connection_manager::ToolInfo;
 use crate::tools::context::ToolInvocation;
@@ -8,17 +5,17 @@ use crate::tools::context::ToolPayload;
 use crate::tools::context::ToolSearchOutput;
 use crate::tools::registry::ToolHandler;
 use crate::tools::registry::ToolKind;
-use crate::tools::spec::mcp_tool_to_deferred_openai_tool;
 use async_trait::async_trait;
 use bm25::Document;
 use bm25::Language;
 use bm25::SearchEngineBuilder;
+use codex_tools::ResponsesApiNamespace;
+use codex_tools::ResponsesApiNamespaceTool;
+use codex_tools::ToolSearchOutputTool;
+use codex_tools::mcp_tool_to_deferred_responses_api_tool;
 use std::collections::BTreeMap;
 use std::collections::HashMap;
 
-#[cfg(test)]
-use crate::client_common::tools::ResponsesApiTool;
-
 pub struct ToolSearchHandler {
     tools: HashMap<String, ToolInfo>,
 }
@@ -129,7 +126,7 @@ fn serialize_tool_search_output_tools(
         let tools = tools
             .iter()
             .map(|tool| {
-                mcp_tool_to_deferred_openai_tool(tool.tool_name.clone(), tool.tool.clone())
+                mcp_tool_to_deferred_responses_api_tool(tool.tool_name.clone(), &tool.tool)
                     .map(ResponsesApiNamespaceTool::Function)
             })
             .collect::<Result<Vec<_>, _>>()?;

codex-rs/core/src/tools/handlers/tool_search_tests.rs

@@ -1,5 +1,6 @@
 use super::*;
 use crate::mcp::CODEX_APPS_MCP_SERVER_NAME;
+use codex_tools::ResponsesApiTool;
 use pretty_assertions::assert_eq;
 use rmcp::model::JsonObject;
 use rmcp::model::Tool;

codex-rs/core/src/tools/spec.rs

@@ -1,6 +1,3 @@
-use crate::client_common::tools::FreeformTool;
-use crate::client_common::tools::FreeformToolFormat;
-use crate::client_common::tools::ResponsesApiTool;
 use crate::client_common::tools::ToolSpec;
 use crate::config::AgentRoleConfig;
 use crate::mcp::CODEX_APPS_MCP_SERVER_NAME;
@@ -46,9 +43,11 @@ use codex_protocol::openai_models::WebSearchToolType;
 use codex_protocol::protocol::SandboxPolicy;
 use codex_protocol::protocol::SessionSource;
 use codex_protocol::protocol::SubAgentSource;
-use codex_tools::ToolDefinition;
+use codex_tools::FreeformTool;
-use codex_tools::parse_dynamic_tool;
+use codex_tools::FreeformToolFormat;
-use codex_tools::parse_mcp_tool;
+use codex_tools::ResponsesApiTool;
+use codex_tools::dynamic_tool_to_responses_api_tool;
+use codex_tools::mcp_tool_to_responses_api_tool;
 use codex_utils_absolute_path::AbsolutePathBuf;
 use codex_utils_template::Template;
 use serde::Deserialize;
@@ -2382,41 +2381,6 @@ fn push_tool_spec(
     }
 }
 
-pub(crate) fn mcp_tool_to_openai_tool(
-    fully_qualified_name: String,
-    tool: rmcp::model::Tool,
-) -> Result<ResponsesApiTool, serde_json::Error> {
-    Ok(tool_definition_to_openai_tool(
-        parse_mcp_tool(&tool)?.renamed(fully_qualified_name),
-    ))
-}
-
-pub(crate) fn mcp_tool_to_deferred_openai_tool(
-    name: String,
-    tool: rmcp::model::Tool,
-) -> Result<ResponsesApiTool, serde_json::Error> {
-    Ok(tool_definition_to_openai_tool(
-        parse_mcp_tool(&tool)?.renamed(name).into_deferred(),
-    ))
-}
-
-fn dynamic_tool_to_openai_tool(
-    tool: &DynamicToolSpec,
-) -> Result<ResponsesApiTool, serde_json::Error> {
-    Ok(tool_definition_to_openai_tool(parse_dynamic_tool(tool)?))
-}
-
-fn tool_definition_to_openai_tool(tool_definition: ToolDefinition) -> ResponsesApiTool {
-    ResponsesApiTool {
-        name: tool_definition.name,
-        description: tool_definition.description,
-        strict: false,
-        defer_loading: tool_definition.defer_loading.then_some(true),
-        parameters: tool_definition.input_schema,
-        output_schema: tool_definition.output_schema,
-    }
-}
-
 /// Builds the tool registry builder while collecting tool specs for later serialization.
 #[cfg(test)]
 pub(crate) fn build_specs(
@@ -2911,7 +2875,7 @@ pub(crate) fn build_specs_with_discoverable_tools(
         entries.sort_by(|a, b| a.0.cmp(&b.0));
 
         for (name, tool) in entries.into_iter() {
-            match mcp_tool_to_openai_tool(name.clone(), tool.clone()) {
+            match mcp_tool_to_responses_api_tool(name.clone(), &tool) {
                 Ok(converted_tool) => {
                     push_tool_spec(
                         &mut builder,
@@ -2930,7 +2894,7 @@ pub(crate) fn build_specs_with_discoverable_tools(
 
     if !dynamic_tools.is_empty() {
         for tool in dynamic_tools {
-            match dynamic_tool_to_openai_tool(tool) {
+            match dynamic_tool_to_responses_api_tool(tool) {
                 Ok(converted_tool) => {
                     push_tool_spec(
                         &mut builder,

codex-rs/core/src/tools/spec_tests.rs

@@ -8,11 +8,11 @@ use crate::tools::ToolRouter;
 use crate::tools::registry::ConfiguredToolSpec;
 use crate::tools::router::ToolRouterParams;
 use codex_app_server_protocol::AppInfo;
-use codex_protocol::dynamic_tools::DynamicToolSpec;
 use codex_protocol::openai_models::InputModality;
 use codex_protocol::openai_models::ModelInfo;
 use codex_protocol::openai_models::ModelsResponse;
 use codex_tools::AdditionalProperties;
+use codex_tools::mcp_tool_to_deferred_responses_api_tool;
 use codex_utils_absolute_path::AbsolutePathBuf;
 use pretty_assertions::assert_eq;
 use std::path::PathBuf;
@@ -64,28 +64,6 @@ fn search_capable_model_info() -> ModelInfo {
     model_info
 }
 
-#[test]
-fn search_tool_deferred_tools_always_set_defer_loading_true() {
-    let tool = mcp_tool(
-        "lookup_order",
-        "Look up an order",
-        serde_json::json!({
-            "type": "object",
-            "properties": {
-                "order_id": {"type": "string"}
-            },
-            "required": ["order_id"],
-            "additionalProperties": false,
-        }),
-    );
-
-    let openai_tool =
-        mcp_tool_to_deferred_openai_tool("mcp__codex_apps__lookup_order".to_string(), tool)
-            .expect("convert deferred tool");
-
-    assert_eq!(openai_tool.defer_loading, Some(true));
-}
-
 #[test]
 fn deferred_responses_api_tool_serializes_with_defer_loading() {
     let tool = mcp_tool(
@@ -102,7 +80,7 @@ fn deferred_responses_api_tool_serializes_with_defer_loading() {
     );
 
     let serialized = serde_json::to_value(ToolSpec::Function(
-        mcp_tool_to_deferred_openai_tool("mcp__codex_apps__lookup_order".to_string(), tool)
+        mcp_tool_to_deferred_responses_api_tool("mcp__codex_apps__lookup_order".to_string(), &tool)
             .expect("convert deferred tool"),
     ))
     .expect("serialize deferred tool");
@@ -127,44 +105,6 @@ fn deferred_responses_api_tool_serializes_with_defer_loading() {
     );
 }
 
-#[test]
-fn dynamic_tool_preserves_defer_loading() {
-    let tool = DynamicToolSpec {
-        name: "lookup_order".to_string(),
-        description: "Look up an order".to_string(),
-        input_schema: serde_json::json!({
-            "type": "object",
-            "properties": {
-                "order_id": {"type": "string"}
-            },
-            "required": ["order_id"],
-            "additionalProperties": false,
-        }),
-        defer_loading: true,
-    };
-
-    let openai_tool = dynamic_tool_to_openai_tool(&tool).expect("convert dynamic tool");
-
-    assert_eq!(
-        openai_tool,
-        ResponsesApiTool {
-            name: "lookup_order".to_string(),
-            description: "Look up an order".to_string(),
-            strict: false,
-            defer_loading: Some(true),
-            parameters: JsonSchema::Object {
-                properties: BTreeMap::from([(
-                    "order_id".to_string(),
-                    JsonSchema::String { description: None },
-                )]),
-                required: Some(vec!["order_id".to_string()]),
-                additional_properties: Some(false.into()),
-            },
-            output_schema: None,
-        }
-    );
-}
-
 fn tool_name(tool: &ToolSpec) -> &str {
     match tool {
         ToolSpec::Function(ResponsesApiTool { name, .. }) => name,

codex-rs/tools/README.md

@@ -5,15 +5,26 @@ shared across multiple crates and does not need to stay coupled to
 `codex-core`.
 
 Today this crate is intentionally small. It currently owns the shared tool
-schema primitives that no longer need to live in `core/src/tools/spec.rs`:
+schema and Responses API tool primitives that no longer need to live in
+`core/src/tools/spec.rs` or `core/src/client_common.rs`:
 
 - `JsonSchema`
 - `AdditionalProperties`
 - `ToolDefinition`
+- `ResponsesApiTool`
+- `FreeformTool`
+- `FreeformToolFormat`
+- `ToolSearchOutputTool`
+- `ResponsesApiNamespace`
+- `ResponsesApiNamespaceTool`
 - `parse_tool_input_schema()`
 - `parse_dynamic_tool()`
 - `parse_mcp_tool()`
 - `mcp_call_tool_result_output_schema()`
+- `tool_definition_to_responses_api_tool()`
+- `dynamic_tool_to_responses_api_tool()`
+- `mcp_tool_to_responses_api_tool()`
+- `mcp_tool_to_deferred_responses_api_tool()`
 
 That extraction is the first step in a longer migration. The goal is not to
 move all of `core/src/tools` into this crate in one shot. Instead, the plan is

codex-rs/tools/src/lib.rs

@@ -1,8 +1,10 @@
-//! Shared tool-schema parsing primitives that can live outside `codex-core`.
+//! Shared tool definitions and Responses API tool primitives that can live
+//! outside `codex-core`.
 
 mod dynamic_tool;
 mod json_schema;
 mod mcp_tool;
+mod responses_api;
 mod tool_definition;
 
 pub use dynamic_tool::parse_dynamic_tool;
@@ -11,4 +13,14 @@ pub use json_schema::JsonSchema;
 pub use json_schema::parse_tool_input_schema;
 pub use mcp_tool::mcp_call_tool_result_output_schema;
 pub use mcp_tool::parse_mcp_tool;
+pub use responses_api::FreeformTool;
+pub use responses_api::FreeformToolFormat;
+pub use responses_api::ResponsesApiNamespace;
+pub use responses_api::ResponsesApiNamespaceTool;
+pub use responses_api::ResponsesApiTool;
+pub use responses_api::ToolSearchOutputTool;
+pub use responses_api::dynamic_tool_to_responses_api_tool;
+pub use responses_api::mcp_tool_to_deferred_responses_api_tool;
+pub use responses_api::mcp_tool_to_responses_api_tool;
+pub use responses_api::tool_definition_to_responses_api_tool;
 pub use tool_definition::ToolDefinition;

codex-rs/tools/src/responses_api.rs

@@ -0,0 +1,102 @@
+use crate::JsonSchema;
+use crate::ToolDefinition;
+use crate::parse_dynamic_tool;
+use crate::parse_mcp_tool;
+use codex_protocol::dynamic_tools::DynamicToolSpec;
+use serde::Deserialize;
+use serde::Serialize;
+use serde_json::Value;
+
+#[derive(Debug, Clone, Serialize, Deserialize, PartialEq)]
+pub struct FreeformTool {
+    pub name: String,
+    pub description: String,
+    pub format: FreeformToolFormat,
+}
+
+#[derive(Debug, Clone, Serialize, Deserialize, PartialEq)]
+pub struct FreeformToolFormat {
+    pub r#type: String,
+    pub syntax: String,
+    pub definition: String,
+}
+
+#[derive(Debug, Clone, Serialize, PartialEq)]
+pub struct ResponsesApiTool {
+    pub name: String,
+    pub description: String,
+    /// TODO: Validation. When strict is set to true, the JSON schema,
+    /// `required` and `additional_properties` must be present. All fields in
+    /// `properties` must be present in `required`.
+    pub strict: bool,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub defer_loading: Option<bool>,
+    pub parameters: JsonSchema,
+    #[serde(skip)]
+    pub output_schema: Option<Value>,
+}
+
+#[derive(Debug, Clone, Serialize, PartialEq)]
+#[serde(tag = "type")]
+pub enum ToolSearchOutputTool {
+    #[allow(dead_code)]
+    #[serde(rename = "function")]
+    Function(ResponsesApiTool),
+    #[serde(rename = "namespace")]
+    Namespace(ResponsesApiNamespace),
+}
+
+#[derive(Debug, Clone, Serialize, PartialEq)]
+pub struct ResponsesApiNamespace {
+    pub name: String,
+    pub description: String,
+    pub tools: Vec<ResponsesApiNamespaceTool>,
+}
+
+#[derive(Debug, Clone, Serialize, PartialEq)]
+#[serde(tag = "type")]
+pub enum ResponsesApiNamespaceTool {
+    #[serde(rename = "function")]
+    Function(ResponsesApiTool),
+}
+
+pub fn dynamic_tool_to_responses_api_tool(
+    tool: &DynamicToolSpec,
+) -> Result<ResponsesApiTool, serde_json::Error> {
+    Ok(tool_definition_to_responses_api_tool(parse_dynamic_tool(
+        tool,
+    )?))
+}
+
+pub fn mcp_tool_to_responses_api_tool(
+    name: String,
+    tool: &rmcp::model::Tool,
+) -> Result<ResponsesApiTool, serde_json::Error> {
+    Ok(tool_definition_to_responses_api_tool(
+        parse_mcp_tool(tool)?.renamed(name),
+    ))
+}
+
+pub fn mcp_tool_to_deferred_responses_api_tool(
+    name: String,
+    tool: &rmcp::model::Tool,
+) -> Result<ResponsesApiTool, serde_json::Error> {
+    Ok(tool_definition_to_responses_api_tool(
+        parse_mcp_tool(tool)?.renamed(name).into_deferred(),
+    ))
+}
+
+pub fn tool_definition_to_responses_api_tool(tool_definition: ToolDefinition) -> ResponsesApiTool {
+    ResponsesApiTool {
+        name: tool_definition.name,
+        description: tool_definition.description,
+        strict: false,
+        defer_loading: tool_definition.defer_loading.then_some(true),
+        parameters: tool_definition.input_schema,
+        output_schema: tool_definition.output_schema,
+    }
+}
+
+#[cfg(test)]
+#[path = "responses_api_tests.rs"]
+mod tests;

codex-rs/tools/src/responses_api_tests.rs

@@ -0,0 +1,173 @@
+use super::ResponsesApiNamespace;
+use super::ResponsesApiNamespaceTool;
+use super::ResponsesApiTool;
+use super::ToolSearchOutputTool;
+use super::dynamic_tool_to_responses_api_tool;
+use super::mcp_tool_to_deferred_responses_api_tool;
+use super::tool_definition_to_responses_api_tool;
+use crate::JsonSchema;
+use crate::ToolDefinition;
+use codex_protocol::dynamic_tools::DynamicToolSpec;
+use pretty_assertions::assert_eq;
+use serde_json::json;
+use std::collections::BTreeMap;
+
+#[test]
+fn tool_definition_to_responses_api_tool_omits_false_defer_loading() {
+    assert_eq!(
+        tool_definition_to_responses_api_tool(ToolDefinition {
+            name: "lookup_order".to_string(),
+            description: "Look up an order".to_string(),
+            input_schema: JsonSchema::Object {
+                properties: BTreeMap::from([(
+                    "order_id".to_string(),
+                    JsonSchema::String { description: None },
+                )]),
+                required: Some(vec!["order_id".to_string()]),
+                additional_properties: Some(false.into()),
+            },
+            output_schema: Some(json!({"type": "object"})),
+            defer_loading: false,
+        }),
+        ResponsesApiTool {
+            name: "lookup_order".to_string(),
+            description: "Look up an order".to_string(),
+            strict: false,
+            defer_loading: None,
+            parameters: JsonSchema::Object {
+                properties: BTreeMap::from([(
+                    "order_id".to_string(),
+                    JsonSchema::String { description: None },
+                )]),
+                required: Some(vec!["order_id".to_string()]),
+                additional_properties: Some(false.into()),
+            },
+            output_schema: Some(json!({"type": "object"})),
+        }
+    );
+}
+
+#[test]
+fn dynamic_tool_to_responses_api_tool_preserves_defer_loading() {
+    let tool = DynamicToolSpec {
+        name: "lookup_order".to_string(),
+        description: "Look up an order".to_string(),
+        input_schema: json!({
+            "type": "object",
+            "properties": {
+                "order_id": {"type": "string"}
+            },
+            "required": ["order_id"],
+            "additionalProperties": false,
+        }),
+        defer_loading: true,
+    };
+
+    assert_eq!(
+        dynamic_tool_to_responses_api_tool(&tool).expect("convert dynamic tool"),
+        ResponsesApiTool {
+            name: "lookup_order".to_string(),
+            description: "Look up an order".to_string(),
+            strict: false,
+            defer_loading: Some(true),
+            parameters: JsonSchema::Object {
+                properties: BTreeMap::from([(
+                    "order_id".to_string(),
+                    JsonSchema::String { description: None },
+                )]),
+                required: Some(vec!["order_id".to_string()]),
+                additional_properties: Some(false.into()),
+            },
+            output_schema: None,
+        }
+    );
+}
+
+#[test]
+fn mcp_tool_to_deferred_responses_api_tool_sets_defer_loading() {
+    let tool = rmcp::model::Tool {
+        name: "lookup_order".to_string().into(),
+        title: None,
+        description: Some("Look up an order".to_string().into()),
+        input_schema: std::sync::Arc::new(rmcp::model::object(json!({
+            "type": "object",
+            "properties": {
+                "order_id": {"type": "string"}
+            },
+            "required": ["order_id"],
+            "additionalProperties": false,
+        }))),
+        output_schema: None,
+        annotations: None,
+        execution: None,
+        icons: None,
+        meta: None,
+    };
+
+    assert_eq!(
+        mcp_tool_to_deferred_responses_api_tool(
+            "mcp__codex_apps__lookup_order".to_string(),
+            &tool,
+        )
+        .expect("convert deferred tool"),
+        ResponsesApiTool {
+            name: "mcp__codex_apps__lookup_order".to_string(),
+            description: "Look up an order".to_string(),
+            strict: false,
+            defer_loading: Some(true),
+            parameters: JsonSchema::Object {
+                properties: BTreeMap::from([(
+                    "order_id".to_string(),
+                    JsonSchema::String { description: None },
+                )]),
+                required: Some(vec!["order_id".to_string()]),
+                additional_properties: Some(false.into()),
+            },
+            output_schema: None,
+        }
+    );
+}
+
+#[test]
+fn tool_search_output_namespace_serializes_with_deferred_child_tools() {
+    let namespace = ToolSearchOutputTool::Namespace(ResponsesApiNamespace {
+        name: "mcp__codex_apps__calendar".to_string(),
+        description: "Plan events".to_string(),
+        tools: vec![ResponsesApiNamespaceTool::Function(ResponsesApiTool {
+            name: "create_event".to_string(),
+            description: "Create a calendar event.".to_string(),
+            strict: false,
+            defer_loading: Some(true),
+            parameters: JsonSchema::Object {
+                properties: Default::default(),
+                required: None,
+                additional_properties: None,
+            },
+            output_schema: None,
+        })],
+    });
+
+    let value = serde_json::to_value(namespace).expect("serialize namespace");
+
+    assert_eq!(
+        value,
+        json!({
+            "type": "namespace",
+            "name": "mcp__codex_apps__calendar",
+            "description": "Plan events",
+            "tools": [
+                {
+                    "type": "function",
+                    "name": "create_event",
+                    "description": "Create a calendar event.",
+                    "strict": false,
+                    "defer_loading": true,
+                    "parameters": {
+                        "type": "object",
+                        "properties": {}
+                    }
+                }
+            ]
+        })
+    );
+}